Page:Popular Science Monthly Volume 42.djvu/76

end of a sitting all the numbers on which, he has been set to work, in the different questions put to him. This experiment, which I saw made at the Salpêtrière, gives really incredible results. A large number of problems were given to M. Inaudi during the afternoon, the data of all of which were preserved in writing, in order to verify the exactness of the repetition. On this day he repeated two hundred and forty-two problems. It is said that he repeated four hundred at a sitting given in the Sorbonne.

These numbers, however, should not be taken as the measure of M. Inaudi's memory for figures, because he did not learn them one after another, without interruption. They were contained in distinct experiments, in which the calculator burdened his memory each time with only twenty-four figures. He therefore had intervals of rest, however brief; and these rests probably facilitated the assimilation of the whole mass, which was really enormous. Usually, he told us, he did not try to retain groups of more than twenty-four figures. One day, twenty-seven were given out to him. That was the maximum number that was essayed. I proposed to him to recite twenty-six, and he was able to repeat them all exactly by employing his usual processes. The experiment tired him a little. After a short rest, I read fifty-two figures to him. In the middle of the experiment, when he had reached the twenty-sixth figure, I pronouncing them and he repeating them, he stopped. He was troubled, and expressed a fear that he would forget the whole. He then repeated rapidly from memory the figures which had just been pronounced, after which he asked me to continue. I went on then to fifty-two figures. He then tried to repeat them all. He did it, but with some transpositions and confusions, and about ten mistakes. The number fifty-two seems to constitute a limit for him.

We have now to examine a little more closely what is meant by the memory for figures; for there are an immense variety of psychological types, and the same mental operation may be comprehended and performed by two persons under absolutely different forms. There are many ways of fixing figures in the memory and calling them out again; or, in other words, several images of a different kind are employed. According to the investigations of the committee of the Academy, M. Inaudi's processes are the contrary of those which arithmetical prodigies are generally supposed to use.

These persons, according to their own testimony, are accustomed to take visual memory as the basis of their mental operations. They have an inner vision of the numbers that are pronounced, and those numbers, during the whole time of the operation, stand before their imaginations as if they were written on a tablet set before their eyes. This process of visualization